Coexistence of spin-density wave and superconductivity in quasi-one-dimensional systems

The possibility of coexistence of two long-range orderings (superconductivity and a spin-density wave) in quasi-one-dimensional magnetic systems is investigated. Allowance is made for deviation from half filling of the band $(\mu=0)$ and transfer processes. It is concluded that the two phases can coexist when the magnetic ordering temperature is higher than the point of the superconducting transition. In addition, it is shown that superconductivity can suppress magnetism if it arises at sufficiently high temperatures. The occurrence of superconductivity in such systems is due to the presence of free carriers above the insulating gap since the spin-density wave has wave vector $Q\neq 2k_F$.